Display device

ABSTRACT

According to one embodiment, a display device includes a substrate, a thin film transistor, a pixel electrode, an organic light emitting layer, a common electrode, and a sealing unit. The thin film transistor is provided on the substrate. The thin film transistor includes a gate electrode, a gate insulating film, a semiconductor film, a first conducting portion, and a second conducting portion. The pixel electrode is electrically connected to one of the first conducting portion and the second conducting portion. The organic light emitting layer is provided on the pixel electrode. The common electrode is provided on the organic light emitting layer. The sealing unit is provided on the common electrode. The sealing unit includes a first sealing film and a second sealing film. A refractive index of the second sealing film is different from a refractive index of the first sealing film.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2012-116835, filed on May 22,2012; the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a display device.

BACKGROUND

There is an active matrix display device in which a switching elementsuch as a thin film transistor controls a current passing through anorganic EL (Electro-Luminescent) device. It is desired to improve imagequality in this display device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view illustrating theconfiguration of a display device according to a first embodiment;

FIG. 2A and FIG. 2B are graphs illustrating the characteristics of adisplay device according to a reference sample;

FIG. 3A and FIG. 3B are graphs illustrating the characteristics of thedisplay device according to the first embodiment;

FIG. 4 is a graph illustrating the characteristics of a hydrogenconcentration of a sealing unit;

FIG. 5A to FIG. 5F are schematic cross-sectional views illustrating amethod for manufacturing the display device according to the firstembodiment;

FIG. 6 is a flowchart illustrating a method for manufacturing thedisplay device according to the first embodiment;

FIG. 7 is a schematic cross-sectional view illustrating theconfiguration of another display device according to the firstembodiment;

FIG. 8 is a schematic view illustrating the configuration of a displaydevice according to a second embodiment;

FIG. 9A and FIG. 9B are graphs illustrating the characteristics of thedisplay device according to the second embodiment; and

FIG. 10A to FIG. 10C are schematic cross-sectional views illustrating amethod for manufacturing the display device according to the secondembodiment.

DETAILED DESCRIPTION

According to one embodiment, a display device includes a substrate, athin film transistor, a pixel electrode, an organic light emittinglayer, a common electrode, and a sealing unit. The thin film transistoris provided on the substrate. The thin film transistor includes a gateelectrode, a gate insulating film, a semiconductor film, a firstconducting portion, and a second conducting portion. The gate electrodeis provided on the substrate. The gate insulating film is provided onthe gate electrode. The semiconductor film is provided on the gateinsulating film. The first conducting portion is electrically connectedto the semiconductor film. The second conducting portion is electricallyconnected to the semiconductor film. The second conducting portion isprovided apart from the first conducting portion. The pixel electrode iselectrically connected to one of the first conducting portion and thesecond conducting portion. The organic light emitting layer is providedon the pixel electrode. The common electrode is provided on the organiclight emitting layer. The sealing unit is provided on the commonelectrode. The sealing unit includes a first sealing film and a secondsealing film. The first sealing film has a hydrogen concentration of10²⁰ atoms/cm³ or less. The second sealing film is stacked on the firstsealing film. The second sealing film has a hydrogen concentration of10²⁰ atoms/cm³ or less. A refractive index of the second sealing film isdifferent from a refractive index of the first sealing film.

Various embodiments will be described hereinafter with reference to theaccompanying drawings.

It is noted that the drawings are schematic or conceptual. Therelationship between the thicknesses and widths of portions, a ratio ofsize between portions, or the like are not necessarily the same as realones. Moreover, even in the case of expressing the same portions,dimensions and ratios between the portions are sometimes expresseddifferently depending on the drawings.

In the specification and drawings, components similar to those describedor illustrated in a drawing thereinabove are marked with the identicalreference numerals, and a detailed description is omitted asappropriate.

First Embodiment

FIG. 1 is a schematic cross-sectional view illustrating theconfiguration of a display device according to a first embodiment.

As shown in FIG. 1, a display device 110 according to the embodimentincludes a substrate 10, a thin film transistor 12, a pixel electrode16, an organic light emitting layer 18, a common electrode 20, and asealing unit 22.

The pixel electrode 16, the organic light emitting layer 18, and thecommon electrode 20 form an organic EL light emitting element portion24. The light emitting element portion 24 is controlled and driven bythe thin film transistor 12. In the display device 110, the combinationsof the switching elements 12 and the light emitting element portions 24are disposed in a matrix configuration. The drive of the switchingelements 12 and the light emission of the light emitting elementportions 24 in association with the drive are controlled to displaypictures. The display device 110 is an active matrix display deviceusing an organic EL device.

The substrate 10 has a major surface 10 a. The substrate 10 includes amain body portion 4 and a barrier layer 5. A light transmissivematerial, for example, is used for the main body portion 4. A glassmaterial or a resin material, for example, is used for the main bodyportion 4. A light transmissive and flexible material can be used forthe main body portion 4. A resin material such as polyimide, forexample, is used for the main body portion 4. The barrier layer 5suppresses the penetration of impurities and moisture through the mainbody portion 4, for example, and protects the thin film transistor 12and the light emitting element portion 24 provided on the substrate 10.A light transmissive and flexible material, for example, is used for thebarrier layer 5.

The thin film transistor 12 is provided on the major surface 10 a of thesubstrate 10.

The thin film transistor 12 includes a first conducting portion 31, asecond conducting portion 32, a gate electrode 33, a gate insulatingfilm 34, a semiconductor film 35, and a channel protection film 36.

The gate electrode 33 is provided on the major surface 10 a of thesubstrate 10. A high melting point metal such as molybdenum tungsten(MoW), molybdenum tantalum (MoTa), and tungsten (W), for example, isused for the gate electrode 33.

The gate insulating film 34 is provided on the gate electrode 33. Inthis example, the gate insulating film 34 is provided on throughout themajor surface 10 a so as to cover the gate electrode 33. An insulativeand light transmissive material, for example, is used for the gateinsulating film 34. One of a silicon oxide film, a silicon nitride film,and a silicon oxynitride film, for example, is used for the gateinsulating film 34.

The semiconductor film 35 is provided on the gate insulating film 34.The gate insulating film 34 is provided between the gate electrode 33and the semiconductor film 35, and insulates the gate electrode 33 fromthe semiconductor film 35. An amorphous oxide semiconductor containingat least one of In, Ga, and Zn, for example, is used for thesemiconductor film 35. Namely, one of an In—Ga—Zn—O oxide semiconductor,an In—Ga—O oxide semiconductor, and an In—Zn—O oxide semiconductor, forexample, is used for the semiconductor film 35. The thickness of thesemiconductor film 35 (a distance along a Z-axis direction) is about 30nm. Thereby, the electric characteristics of the semiconductor film 35can be improved, for example. More specifically, the thickness of thesemiconductor film 35 is 5 nm or more and 50 nm or less, for example.

In the semiconductor film 35 including an amorphous oxide semiconductor,a diffraction pattern or the like showing crystallinity is not observedeven though the semiconductor film 35 is observed using a transmissionelectron microscope (TEM) or X-ray diffraction (XRD) topography, forexample. The film and shape of the semiconductor film 35 can be observedusing a scanning electron microscope (SEM), TEM, or the like.

For the semiconductor film 35, such a material may be used that themicrocrystals of the oxide semiconductor are dispersed in the amorphousoxide semiconductor described above.

The first conducting portion 31 is provided on the gate insulating film34. A part of the first conducting portion 31 is provided on thesemiconductor film 35, and contacts the semiconductor film 35. Thus, thefirst conducting portion 31 is electrically connected to thesemiconductor film 35. The second conducting portion 32 is provided onthe gate insulating film 34. The second conducting portion 32 isdisposed apart from the first conducting portion 31. A part of thesecond conducting portion 32 is provided on the semiconductor film 35,and contacts the semiconductor film 35. Thus, the second conductingportion 32 is electrically connected to the semiconductor film 35. Ti,Al, Mo, and the like, for example, are used for the first conductingportion 31 and the second conducting portion 32. The first conductingportion 31 and the second conducting portion 32 may be a stacked bodycontaining at least one of Ti, Al, and Mo, for example. The firstconducting portion 31 is one of the source electrode and drain electrodeof the thin film transistor 12. The second conducting portion 32 is theother of the source electrode and drain electrode of the thin filmtransistor 12.

The channel protection film 36 is provided on the semiconductor film 35.The channel protection film 36 protects the semiconductor film 35. Asilicon oxide film, for example, is used for the channel protection film36.

The first conducting portion 31 covers a first portion 36 a of thechannel protection film 36. The second conducting portion 32 covers asecond portion 36 b of the channel protection film 36. The firstconducting portion 31 covers a first region 35 a of the semiconductorfilm 35. The second conducting portion 32 covers a second region 35 b ofthe semiconductor film 35. The semiconductor film 35 has a third region35 c that is not covered with the first conducting portion 31 and thesecond conducting portion 32. The gate electrode 33 has a portion 33 abetween the first conducting portion 31 and the second conductingportion 32 when seen in a direction vertical to a film surface 35 p ofthe semiconductor film 35 (hereinafter, referred to as the Z-axisdirection). Namely, the gate electrode 33 opposes the third region 35 cof the semiconductor film 35 with the gate insulating film 34 sandwichedbetween the gate electrode 33 and the third region 35 c. The channelprotection film 36 is provided at least on the third region 35 c. Thus,a voltage is applied to the gate electrode 33 to generate a channelthrough the semiconductor film 35, and a current passes across the firstconducting portion 31 and the second conducting portion 32.

A passivation film 40 is provided between the thin film transistor 12and the pixel electrode 16. An insulative and light transmissivematerial, for example, is used for the passivation film 40. One of asilicon oxide film, a silicon nitride film, and a silicon oxynitridefilm, for example, is used for the passivation film 40.

In this example, a color filter 44 is provided between the pixelelectrode 16 and the passivation film 40. The color filter 44 has adifferent color for every pixel. The transmittance of the color filter44 is varied depending on wavelengths. For example, one of red, green,and blue color resin films (a color resist, for example) is used for thecolor filter 44. The color filter 44 is provided as necessary. The colorfilter 44 can be omitted.

The pixel electrode 16 is electrically connected to one of the firstconducting portion 31 and the second conducting portion 32. In thisexample, the pixel electrode 16 is electrically connected to the firstconducting portion 31 (a source, for example).

The pixel electrode 16 is provided on the color filter 44. The pixelelectrode 16 has an opposing region 16 a opposing the thin filmtransistor 12 and a non-opposing region 16 b not opposing the thin filmtransistor 12 in the Z-axis direction. An electrically conductive andlight transmissive material, for example, is used for the pixelelectrode 16. ITO (Indium Tin Oxide) or the like, for example, is usedfor the pixel electrode 16. A metal oxide such as ITO, IZO (In—Zn—O),AZO (Al—Zn—O), IGZO (In—Ga—Zn—O), and ZnO, for example, is used for thepixel electrode 16. The pixel electrode 16 is also referred to as apixel electrode, for example.

The passivation film 40 and the color filter 44 are provided with anopening 40 a (a first opening) and an opening 44 a, respectively, and apart 31 p of the first conducting portion 31 is exposed from the opening40 a and the opening 44 a. A part 16 c of the opposing region 16 a ofthe pixel electrode 16 contacts the part 31 p of the first conductingportion 31 in the opening 40 a and the opening 44 a. Thus, the pixelelectrode 16 is electrically connected to the first conducting portion31.

A planarization film 42 is provided on the pixel electrode 16 and thecolor filter 44. An insulative material, for example, is used for theplanarization film 42. An organic resin material, for example, is usedfor the planarization film 42. The planarization film 42 is providedwith an opening 42 a (a second opening). A part 16 p of the non-opposingregion 16 b of the pixel electrode 16 is exposed from the opening 42 a.

The organic light emitting layer 18 is provided on the planarizationfilm 42. The organic light emitting layer 18 contacts the part 16 p ofthe non-opposing region 16 b of the pixel electrode 16 in the opening 42a. The planarization film 42 prevents the opposing region 16 a fromcontacting the organic light emitting layer 18. A stacked body having ahole transport layer, a light emitting layer, and an electron transportlayer stacked on each other, for example, is used for the organic lightemitting layer 18.

The common electrode 20 is provided on the organic light emitting layer18. The common electrode 20 has a portion 20 a extending on thesemiconductor film 35. A conductive material is used for the commonelectrode 20. A metal material such as Al and MgAg, for example, is usedfor the common electrode 20. The thickness of the common electrode 20 is200 nm, for example, (100 nm or more and 300 nm or less, for example).

The light emitting element portion 24 is formed in the non-opposingregion 16 b, for example. In the light emitting element portion 24, avoltage is applied across the pixel electrode 16 and the commonelectrode 20 to emit light from the organic light emitting layer 18. Thelight emitted from the organic light emitting layer 18 passes throughthe color filter 44, the passivation film 40, the gate insulating film34, and the substrate 10, and goes to the outside. The display device110 is a lower surface emitting display device.

The sealing unit 22 is provided on the common electrode 20. The sealingunit 22 includes a first sealing film 51 and a second sealing film 52.The first sealing film 51 is provided on the common electrode 20. Thesecond sealing film 52 is stacked on the first sealing film 51. In thisexample, the second sealing film 52 is provided on the first sealingfilm 51. In the sealing unit 22, the organic light emitting layer 18 andthe common electrode 20 is covered with the first sealing film 51 andthe second sealing film 52. The sealing unit 22 protects the organiclight emitting layer 18 and the common electrode 20. The hydrogenconcentration of the first sealing film 51 is 10²⁰ atoms/cm³ or less.The hydrogen concentration of the second sealing film 52 is 10²⁰atoms/cm³ or less. An inorganic material, for example, is used for thefirst sealing film 51 and the second sealing film 52. At least one ofsilicon oxide, silicon oxynitride, silicon nitride, aluminum oxide(alumina), and tantalum oxide, for example, is used for the firstsealing film 51 and the second sealing film 52.

The first sealing film 51 has compressive stress, and the second sealingfilm 52 has tensile stress. Alternatively, the first sealing film 51 hastensile stress, and the second sealing film 52 has compressive stress.Namely, the first sealing film 51 has one of compressive stress andtensile stress. The second sealing film 52 has the other of compressivestress and tensile stress.

For example, a composition (a compound, for example) used for the secondsealing film 52 is substantially the same as a composition (a compound,for example) used for the first sealing film 51. For example, the firstsealing film 51 and the second sealing film 52 contain substantially thesame material. When using the same composition, the refractive indexesof these films are different from each other if stresses applied tothese films are different.

The refractive index of the second sealing film 52 is different from therefractive index of the first sealing film 51. For example, therefractive index of the second sealing film 52 is lower than therefractive index of the first sealing film 51. When the refractive indexof the second sealing film 52 is lower than the refractive index of thefirst sealing film 51, the second sealing film 52 has tensile stress,and the first sealing film 51 has compressive stress. Alternatively, therefractive index of the second sealing film 52 is higher than therefractive index of the first sealing film 51. When the refractive indexof the second sealing film 52 is higher than the refractive index of thefirst sealing film 51, the second sealing film 52 has compressivestress, and the first sealing film 51 has tensile stress. In thefollowing, the case will be described where the refractive index of thesecond sealing film 52 is lower than the refractive index of the firstsealing film 51. The first sealing film 51 and the second sealing film52 are an oxide containing Si. When the first sealing film 51 and thesecond sealing film 52 are an oxide containing Si, the refractive indexof the first sealing film 51 is 1.46, for example, and the refractiveindex of the second sealing film 52 is 1.42, for example. The refractiveindexes of the first sealing film 51 and the second sealing film 52 canbe measured by ellipsometry, for example. A difference between therefractive indexes of the first sealing film 51 and the second sealingfilm 52 (a difference between compressive stress and tensile stress) canbe implemented by changing the film forming conditions, for example.

The order of stacking the first sealing film 51 and the second sealingfilm 52 is not limited to the description recited above. Such aconfiguration may be possible in which the second sealing film 52 isprovided on the common electrode 20 and the first sealing film 51 isstacked on the second sealing film 52. A plurality of compressive stressfilms are alternately stacked on a plurality of tensile stress films asdescribed later.

FIG. 2A and FIG. 2B are graphs illustrating the characteristics of adisplay device according to a reference sample.

FIG. 2A and FIG. 2B illustrate the characteristics of the display deviceaccording to the reference sample in which a sealing film having thehydrogen concentration higher than 10²⁰ atom s/cm³ is provided on acommon electrode 20. The configuration of this display device is thesame as the display device 110 except the hydrogen concentrationincluded in the sealing film.

The horizontal axis in FIG. 2A and FIG. 2B expresses a gate voltage Vg(V) applied to the gate electrode 33 of the thin film transistor 12. Thevertical axis expresses a current Id (A) passing across the firstconducting portion 31 and the second conducting portion 32 of the thinfilm transistor 12 (a current passing across the drain and the source).FIG. 2A expresses the voltage-current characteristics before forming thesealing film. FIG. 2B expresses the voltage-current characteristicsafter forming the sealing film.

As shown in FIG. 2A, in the initial characteristics before forming thesealing film, excellent transistor characteristics are obtained.However, as shown in FIG. 2B, when the sealing film having the hydrogenconcentration higher than 10²⁰ atoms/cm³ is formed, the thresholdvoltage of the thin film transistor 12 is reduced. Because of thereduction, in the reference sample, it is difficult to perform desiredcontrol, and the image quality of the display device is poor.

FIG. 3A and FIG. 3B are graphs illustrating the characteristics of thedisplay device according to the first embodiment.

The horizontal axis in FIG. 3A and FIG. 3B expresses the gate voltageVg, and the vertical axis expresses the current Id. FIG. 3A expressesthe voltage-current characteristics before forming the sealing unit 22,and FIG. 3B expresses the voltage-current characteristics after formingthe sealing unit 22.

As shown in FIG. 3A and FIG. 3B, in the display device 110 according tothe embodiment, even after forming the sealing unit 22, the fluctuationof the threshold voltage of the thin film transistor 12 was notobserved. In the display device 110, higher image quality can beobtained than in the conventional display device.

FIG. 4 is a graph illustrating the characteristics of a hydrogenconcentration of the sealing unit.

The horizontal axis in FIG. 4 expresses a hydrogen concentration Hc ofthe sealing unit 22. The vertical axis in FIG. 4 expresses a fluctuationvalue Vs (volt: V) of the threshold voltage of the thin film transistor12 before and after forming the sealing unit 22.

As shown in FIG. 4, in the case where the concentration Hc is about7×10¹⁹ atoms/cm³, the fluctuation value Vs is about +1 V. When theconcentration Hc is 1.5×10²¹ atoms/cm³, the fluctuation value Vs isabout −9V. When the concentration Hc is 0.6×10²² atoms/cm³, thefluctuation value Vs is about −22 V. When the concentration Hc is high,the fluctuation value Vs is shifted to the negative side, and theabsolute value of the fluctuation value Vs is increased. When theconcentration Hc is 1×10²⁰ atoms/cm³, the fluctuation value Vs issubstantially zero.

The inventor prepared thin film transistors in various configurations,and evaluated the fluctuation of the threshold voltage. As a result, theinventor found that the fluctuation of the threshold voltage is small inthe configuration in which a sealing film having a hydrogenconcentration of about 1×10²⁰ atoms/cm³ or less is used. The inventorestimated from this result that the fluctuation of the threshold voltageof the thin film transistor 12 is caused by hydrogen contained in thesealing unit 22.

The sealing unit 22 including the first sealing film 51 and the secondsealing film 52 having a hydrogen concentration of 1×10²⁰ atoms/cm³ orless is provided to reduce the fluctuation of the threshold voltage ofthe thin film transistor 12. Preferably, the hydrogen concentration ofthe first sealing film 51 and the second sealing film 52 is 7×10¹⁹atoms/cm³ or less. Thereby, the hydrogen concentration of the sealingfilm can be suppressed, and the fluctuation of the threshold voltage ofthe thin film transistor 12 can be suppressed, even in the case wherevarious conditions in the manufacturing process steps are varied, forexample.

It was revealed that at least one of a silicon oxide film, a siliconoxynitride film, a silicon nitride film, alumina, and a tantalum oxidefilm, which are excellent in stability, is used for the sealing film andthe hydrogen concentration is made 10²⁰ atoms/cm³ or less in these filmsto stabilize the thin film transistor the characteristics.

A sealing film in this configuration is used to obtain excellentcharacteristics. However, for example, in the case where one layer (onetype) of a sealing film is formed as the sealing film recited above,peeling occurs in an interface between the common electrode and thesealing film, or an interface between the pixel electrode and the commonelectrode, for example. It can be considered that this peeling is causedby a stress occurring in the sealing film.

Compressive stress or tensile stress remains in the sealing filmdepending on the process conditions in forming the sealing film. Whenstress remains in the sealing film, the peeling occurs in theconfiguration in which a sealing film having only one stress is formed,for example.

In the embodiment, a plurality of sealing films are formed on purpose.It was revealed that the stress type is varied in the sealing films tosolve this problem. As described above, a stacked structure includingthe first sealing film 51 having one of compressive stress and tensilestress and the second sealing film 52 having the other of compressivestress and tensile stress is used as the sealing unit 22, therebyenabling the suppression of the adverse effect of stress occurring inthe sealing unit 22 on the organic light emitting layer 18.

The stresses of the first sealing film 51 and the second sealing film 52can be controlled by controlling at least one of a gas pressure, apartial pressure ratio, input power, substrate temperature, and adistance between a target and a substrate in forming the sealing film,for example.

It is considerably difficult to reduce the stress in a single sealingfilm in consideration of variations in the manufacturing conditions. Onthe contrary, a plurality of sealing films having different types ofstresses is used to practically make variations smaller for facilitatingthe control of stress.

FIG. 5A to FIG. 5F are schematic cross-sectional views illustrating amethod for manufacturing the display device according to the firstembodiment.

As shown in FIG. 5A, in the manufacture of the display device 110, thethin film transistor 12 is formed on the major surface 10 a of thesubstrate 10. In forming the thin film transistor 12, the gate electrode33 is formed on the major surface 10 a. The gate insulating film 34 isformed on the major surface 10 a and the gate electrode 33. Thesemiconductor film 35 is formed on the gate insulating film 34. Thechannel protection film 36 is formed on the semiconductor film 35. Thefirst conducting portion 31 and the second conducting portion 32 areformed on the gate insulating film 34, the semiconductor film 35, andthe channel protection film 36.

As shown in FIG. 5B, the passivation film 40 is formed on the thin filmtransistor 12. For example, a SiO₂ film to be the passivation film 40 isformed by PE-CVD (Plasma-Enhanced Chemical Vapor Deposition). Theopening 40 a is formed in the SiO₂ film. Thus, the passivation film 40is obtained. The thickness of the passivation film 40 is 200 nm (100 nmor more 300 m or less), for example.

The color filter 44 is formed on the passivation film 40. For example,one of red, green, and blue color resin films (a color resist, forexample) is applied. The color resin film is patterned, and the opening44 a is formed. Thus, the color filter 44 is obtained. The thickness ofthe color filter 44 is 2 μm, for example (1 μm or more and 3 m or less,for example).

The pixel electrode 16 is formed on the color filter 44. For example, anITO film to be the pixel electrode 16 is formed by sputtering or thelike, and patterned in a predetermined shape to obtain the pixelelectrode 16. The thickness of the pixel electrode 16 is 60 nm (30 nm ormore and 200 nm or less), for example.

As shown in FIG. 5C, the planarization film 42 is formed on the pixelelectrode 16 and the color filter 44. For example, an organic resin tobe the planarization film 42 is applied and patterned to obtain theplanarization film 42. The organic light emitting layer 18 is formed onthe planarization film 42 and the non-opposing region 16 b of the pixelelectrode 16. The organic light emitting layer 18 is formed by vapordeposition, for example.

As shown in FIG. 5D, the common electrode 20 is formed on the organiclight emitting layer 18. A LiF film is stacked on an Al film to obtainthe common electrode 20, for example. Vapor deposition, for example, isused for forming the common electrode 20.

As shown in FIG. 5E, the first sealing film 51 is formed on the commonelectrode 20. At least one of a silicon oxide film, a silicon oxynitridefilm, a silicon nitride film, alumina, and a tantalum oxide film, forexample, to be the first sealing film 51 is formed by sputtering, forexample, to obtain the first sealing film 51. A gas pressure in formingthe first sealing film 51 is about a pressure of 0.5 Pa, for example, (apressure of 0.1 Pa or more and less than a pressure of 2.0 Pa, forexample).

As shown in FIG. 5F, the second sealing film 52 is formed on the firstsealing film 51. At least one of a silicon oxide film, a siliconoxynitride film, a silicon nitride film, alumina, and a tantalum oxidefilm, for example, to be the second sealing film 52 is formed bysputtering, for example, to obtain the second sealing film 52. A gaspressure in forming the second sealing film 52 is about a pressure of3.0 Pa, for example (a pressure of 2.0 Pa or more and a pressure of 10.0Pa or less, for example). Thus, the sealing unit 22 is formed on thecommon electrode 20. As described above, the display device 110 isfabricated. As described above, a gas pressure in forming the secondsealing film 52 is made higher than a gas pressure in forming the firstsealing film 51, thereby enabling tensile stress to be generated in thesecond sealing film 52.

FIG. 6 is a flowchart illustrating a method for manufacturing thedisplay device according to the first embodiment.

As shown in FIG. 6, the method for manufacturing the display device 110includes Step S110 of forming the thin film transistor 12, Step S120 offorming the pixel electrode 16, Step S130 of forming the organic lightemitting layer 18, Step S140 of forming the common electrode 20, andStep S150 of forming the sealing unit 22.

In Step S110, the process described with reference to FIG. 5A isperformed, for example. In Step S120, the process described withreference to FIG. 5B is performed, for example. In Step S130, theprocess described with reference to FIG. 5C is performed, for example.In Step S140, the process described with reference to FIG. 5D isperformed, for example. In Step S150, the processes described withreference to FIG. 5E and FIG. 5F are performed, for example.

FIG. 7 is a schematic cross-sectional view illustrating theconfiguration of another display device according to the firstembodiment.

As shown in FIG. 7, a sealing unit 22 of a display device 112 includes astacked film 54.

The stacked film 54 includes a plurality of first sealing films 51 and aplurality of second sealing films 52. The first sealing films 51 and thesecond sealing films 52 are alternately stacked on each other in theZ-axis direction.

Also in the display device 112 including the stacked film 54 in thesealing unit 22, the hydrogen concentration of the first sealing film 51and the second sealing film 52 is 10²⁰ atoms/cm³ or less, therebyenabling the suppression of the fluctuation of the threshold voltage ofthe thin film transistor 12 to improve the image quality of the displaydevice 112.

The barrier properties of the sealing unit 22 to the organic lightemitting layer 18 can be enhanced by using the stacked film 54 as thesealing unit 22. In the stacked film 54, the balance of the compressivestress included in the first sealing film 51 and the tensile stressincluded in the second sealing film 52 is made more uniform. Thereby,the adverse effect of the stress included in the sealing unit 22 on theorganic light emitting layer 18 can be more appropriate suppressed.

Second Embodiment

FIG. 8 is a schematic view illustrating the configuration of a displaydevice according to a second embodiment.

As shown in FIG. 8, a display device 210 includes an organic barrierlayer 46 between a common electrode 20 and a sealing unit 22. Theorganic barrier layer 46 is an organic film containing at leastpolyparaxylene, for example. The configuration of the display device 210is the same as the configuration of the display device 110 except thatthe organic barrier layer 46 is provided.

The organic barrier layer 46 protects an organic light emitting layer 18from oxygen plasma used when forming a first sealing film 51 and asecond sealing film 52 that are inorganic films. Thereby, a damage onthe organic light emitting layer 18 can be suppressed. The organicbarrier layer 46 is provided to form a conformal film in the sealingunit 22. For example, the organic barrier layer 46 fills a defect suchas a pin hole. Thereby, the barrier performance of the sealing unit 22and the organic barrier layer 46 can be improved. The coverage of theorganic barrier layer 46 can be made higher than the coverage of thefirst sealing film 51 and the second sealing film 52. Thereby, a muchhigher barrier performance can be obtained.

FIG. 9A and FIG. 9B are graphs illustrating the characteristics of thedisplay device according to the second embodiment.

The horizontal axis in FIG. 9A and FIG. 9B expresses the gate voltageVg, and the vertical axis expresses the current Id. FIG. 9A and FIG. 9Bexpress the voltage-current characteristics before and after forming thesealing unit 22 and the organic barrier layer 46, respectively.

FIG. 9A and as shown in FIG. 9B, in the display device 210 according tothe embodiment, fluctuations are not observed in the threshold voltageof a thin film transistor 12 after forming the sealing unit 22 and theorganic barrier layer 46. As described above, also in the display device210 provided with the organic barrier layer 46, the fluctuation of thethreshold voltage of the thin film transistor 12 can be suppressed, andthe image quality can be improved.

FIG. 10A to FIG. 10C are schematic cross-sectional views illustrating amethod for manufacturing the display device according to the secondembodiment.

In the method for manufacturing the display device 210, since theprocedures from the start to forming the common electrode 20 aresubstantially the same as the procedures of the display device 110, adescription is omitted

As shown in FIG. 10A, the organic barrier layer 46 is formed on thecommon electrode 20. The organic barrier layer 46 is formed by thermalCVD (Chemical Vapor Deposition), for example.

As shown in FIG. 10B, the first sealing film 51 is formed on the organicbarrier layer 46. As described in the display device 110, the firstsealing film 51 is formed by sputtering. A gas pressure in forming thefirst sealing film 51 is about a pressure of 0.5 Pa, for example (apressure of 0.1 Pa or more and less than a pressure of 2.0 Pa, forexample).

As shown in FIG. 10C, the second sealing film 52 is formed on the firstsealing film 51. As described in the display device 110, the secondsealing film 52 is formed by sputtering. A gas pressure in forming thesecond sealing film 52 is about a pressure of 3.0 Pa (a pressure of 2.0Pa or more and less than a pressure of 10.0 Pa, for example). Thus, thesealing unit 22 is formed on the organic barrier layer 46. As describedabove, the display device 210 is fabricated.

In the description recited above in the embodiment, the lower surfaceemitting display device is described. However, in the embodiment, thedisplay device may be a top surface emission type.

According to the embodiment, a display device with a high image qualitycan be provided.

In the specification of the application, a state in which “a componentis provided on another component” includes a state in which a componentis directly provided on another component as well as a state in which acomponent is provided on another component with a different elementinserted between the component and another component. A state in which“a component is stacked on another component” includes a state in whicha component is stacked on another component to contact each other aswell as a state in which a component is stacked on another componentwith a different element inserted between the component and anothercomponent. A state in which “a component opposes another component”includes a state in which a component directly faces another componentas well as a state in which a component faces another component with adifferent element inserted between the component and another component.

As described above, the embodiments of the invention are described withreference to specific examples.

However, the embodiments of the invention are not limited to thesespecific examples. For example, the specific configurations of thecomponents such as the substrate, the thin film transistor, the pixelelectrode, the organic light emitting layer, the common electrode, thesealing unit, the first sealing film, the second sealing film, theorganic barrier layer, and the stacked film included in the displaydevice are incorporated in the scope of the invention as long as aperson skilled in the art appropriately selects components from thepublicly known range to similarly implement the invention for obtainingthe similar effect.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the invention.

What is claimed is:
 1. A display device, comprising: a substrate; a thinfilm transistor provided on the substrate, the thin film transistorincluding: a gate electrode provided on the substrate; a gate insulatingfilm provided on the gate electrode; a semiconductor film provided onthe gate insulating film, the semiconductor film including an oxidesemiconductor containing at least one of In, Ga, and Zn; a firstconducting portion electrically connected to the semiconductor film; anda second conducting portion electrically connected to the semiconductorfilm and provided apart from the first conducting portion; a pixelelectrode electrically connected to one of the first conducting portionand the second conducting portion; an organic light emitting layerprovided on the pixel electrode; a common electrode provided on theorganic light emitting layer; and a sealing unit provided on the commonelectrode, the sealing unit including: a first sealing film having ahydrogen concentration of 10²⁰ atoms/cm³ or less; and a second sealingfilm stacked on the first sealing film and having a hydrogenconcentration of 10²⁰ atoms/cm³ or less, a refractive index of thesecond sealing film being different from a refractive index of the firstsealing film.
 2. The device according to claim 1, wherein the firstsealing film has one of compressive stress and tensile stress, and thesecond sealing film has the other of compressive stress and tensilestress.
 3. The device according to claim 1, further comprising anorganic barrier layer provided between the common electrode and thesealing unit and containing at least polyparaxylene.
 4. The deviceaccording to claim 1, wherein the sealing unit includes a plurality ofthe first sealing films and a plurality of the second sealing films, andthe plurality of the first sealing films and the plurality of the secondsealing films are alternately stacked on each other.
 5. The deviceaccording to claim 1, wherein the first sealing film and the secondsealing film contain at least one of silicon oxide, silicon oxynitride,silicon nitride, aluminum oxide, and tantalum oxide.
 6. The deviceaccording to claim 1, wherein the first sealing film and the secondsealing film contain same material.
 7. The device according to claim 1,wherein a thickness of the semiconductor film is 5 nm or more and 50 nmor less.
 8. The device according to claim 1, wherein a hydrogenconcentration of the first sealing film is 7×10¹⁹ atoms/cm³ or less, anda hydrogen concentration of the second sealing film is 7×10¹⁹ atoms/cm³or less.
 9. The device according to claim 1, wherein the commonelectrode extends on the semiconductor film.
 10. The device according toclaim 1, wherein the substrate is flexible.
 11. The device according toclaim 1, wherein the semiconductor film has a first region covered withthe first conducting portion, a second region covered with the secondconducting portion, and a third region not covered with the firstconducting portion and the second conducting portion, and the gateelectrode opposes the third region with the gate insulating filmsandwiched between the gate electrode and the third region.
 12. Thedevice according to claim 11, wherein the thin film transistor furtherincludes a channel protection film provided at least on the thirdregion.
 13. The device according to claim 12, wherein the channelprotection film includes a silicon oxide film.
 14. The device accordingto claim 1, wherein the pixel electrode contains at least one of ITO,IZO, AZO, IGZO, and ZnO.
 15. The device according to claim 1, wherein athickness of the pixel electrode is 30 nm or more and 200 nm or less.16. The device according to claim 1, further comprising an insulativeand light transmissive passivation film provided between the thin filmtransistor and the pixel electrode, the passivation film having a firstopening, a part of the first conducting portion being exposed from thefirst opening, the pixel electrode contacting the part of the firstconducting portion in the first opening.
 17. The device according toclaim 1, further comprising a planarization film provided between thepixel electrode and the organic light emitting layer, the pixelelectrode including an opposing region opposing the thin filmtransistor, and a non-opposing region not opposing the thin filmtransistor, the planarization film having a second opening, a part ofthe non-opposing region being exposed from the second opening, theorganic light emitting layer contacting the part of the non-opposingregion in the second opening.
 18. The device according to claim 1,wherein the common electrode includes a metal material.
 19. The deviceaccording to claim 18, wherein the common electrode contains at leastone of Al and MgAg.